Various dicyclopentadiene cracking methods are known. The dissociation to the monomer is a monomolecular reaction. The cracking can be accomplished by distilling dicyclopentadiene under atmospheric pressure. Dicyclopentadiene boils at 170.degree. C. It cracks at a rate of 36% per hour at 170.degree. C. Monomer is obtained by maintaining the top temperature of the fractionating column at 41.degree.-42.degree. C.
Another procedure involves adding dicyclopentadiene to a hot liquid, e.g., a high boiling oil at 250.degree.-260.degree. C. The resulting vapors are fractionated to remove refluxing uncracked dimer and entrained liquid. A commercial procedure entails vapor phase cracking at 350.degree.-400.degree. C. See, generally, "Cyclopentadiene and Dicyclopentadiene", Kirk-Othmer: Encyclopedia of Chemical Technology, Vol. 7 , 3d Ed., p. 424 (1979); and U.S. Pat. Nos. 2,453,044; 2,490,866; 3,007,978; 3,544,644; 3,719,718 and 4,048,242.